APS SOFTWARE AND ELECTRONICS

Analog and Digital Electronics Embedded Computing and assocoitated Software including RTOS for PIC1XF1XXX[X]

Using I2C bus over large distances

The Inter Inter Circuit Bus or I2C bus is a true bus system for microprocessors. Any node on the
bus can be a master or a slave. The address structure is either 7 or 10 bits with the 7 bits
occupying the upper 8 bits of the byte and the LSB bit is used to indicate a read (1) or a write (0).
Most I2C busses are less than 1 meter in length. Up to 128 individual addresses can be used on the
7 bit addressed bus and 1024 on the 10 bit bus. It is a shame to limit this bus to 1 meter when it
can be extended to many meters to control whole sub systems.
Certain products currently appearing and that will appear in the future on this site are I2C slaves.
The product "Serial RS232 to I2c Master" allows a PC to control I2C slaves as if the PC was an
embedded computer. Fairly large lengths of the I2C bus can be achieved using the NXP P82B96 buffer
chip. The product "I2C High Voltage / Long Distance" converts I2C voltages and signals from 3.3 or
5 Volts to 12 volts and back again. This device will allow data rates greater than 200 KHz over
lengths of flat "Silver Satin" 4 wire telephone cable of over 250 meters. Thus the concept and
use of the I2C bus can be expanded to such things as control of water valves and moisture
detection over a backyard or greenhouse setting. Anything that can be controlled by the I2C bus
can be expanded over great distances and the uses are endless.